Generally, the process for manufacturing integrated circuits on a silicon wafer substrate typically involves deposition of a thin dielectric or conductive film on the wafer using oxidation or any of a variety of chemical vapor deposition processes; formation of a circuit pattern on a layer of photoresist material by photolithography; placing a photoresist mask layer corresponding to the circuit pattern on the wafer; etching of the circuit pattern in the conductive layer on the wafer; and stripping of the photoresist mask layer from the wafer. Each of these steps, particularly the photoresist stripping step, provides abundant opportunity for organic, metal and other potential circuit-contaminating particles to accumulate on the wafer surface.
In the semiconductor fabrication industry, minimization of particle contamination on semiconductor wafers increases in importance as the integrated circuit devices on the wafers decrease in size. With the reduced size of the devices, a contaminant having a particular size occupies a relatively larger percentage of the available space for circuit elements on the wafer as compared to wafers containing the larger devices of the past. Moreover, the presence of particles in the integrated circuits compromises the functional integrity of the devices in the finished electronic product.
Currently, mini-environment based IC manufacturing facilities are equipped to control airborne particles much smaller than 1.0 μm, as surface contamination continues to be of high priority to semiconductor manufacturers. To achieve an ultraclean wafer surface, particles must be removed from the wafer, and particle-removing methods are therefore of utmost importance in the fabrication of semiconductors.
The most common system for cleaning semiconductor wafers during wafer processing includes a series of tanks which contain the necessary cleaning solutions and are positioned in a “wet bench” in a clean room. Batches of wafers are moved in sequence through the tanks, typically by operation of a computer-controlled automated apparatus. Currently, semiconductor manufacturers use wet cleaning processes which may use cleaning agents such as deionized water and/or surfactants.
Other wafer-cleaning processes utilize solvents, dry cleaning using high-velocity gas jets, and a megasonic cleaning process, in which very high-frequency sound waves are used to dislodge particles from the wafer surface. Cleaning systems which use deionized (DI) water currently are widely used in the industry because the systems are effective in removing particles from the wafers and are relatively cost-efficient. Approximately 4.5 tons of water are used for the production of each 200-mm, 16-Mbit, DRAM wafer.
A conventional wet bench system 8 is shown schematically in FIG. 1. The system 8 includes wet bench tanks 10a, 10b, 10c. The first tank 10a and second tank 10b each typically contains a basic ACT organic solvent solution (not shown) in which multiple wafers 16 are immersed for the stripping of photoresist from each of the wafers 16. In the third wet bench tank 10c, the wafers 16 are typically rinsed with an aqueous acidic NOE solution, which removes photoresist residues and particles from the wafers 16 after the wafers 16 are immersed in the basic ACT solutions in the first tank 10a and second tank 10b, for example. Typical other uses for the system 8 include SPM cleaning, APM cleaning and M2 etch/cleaning, for example.
Each tank 10a, 10b, 10c includes tank walls 12 that define a tank interior 14 which receives the multiple wafers 16. As shown in FIG. 2, the first tank 10a, as well as the second tank 10b and third tank 10c, typically includes a top opening 15 which is reversibly closed by a pair of half-lid panels 18 hingedly attached to respective opposing tank walls 12. When closed, the half-lid panels 18 are separated by a lid gap 20. In another design, shown in FIG. 3, each wet bench cleaning tank 22 includes a full-lid panel 24 which is hingedly attached to one of the tank walls 12 to reversibly close the top opening 15.
In operation of the system 8, a wafer boat or other wafer support (not illustrated), which typically holds up to fifty of the semiconductor wafers 16 in horizontally-adjacent relationship to each other, is sequentially placed in the tank interiors 14 of the wet bench tanks 10a, 10b, 10c, respectively. The wafers 16 are initially immersed in the basic first ACT solution (not shown) contained in the first tank 10a for the stripping of photoresist from the wafers 16 after a photolithography process is carried out on the wafers 16.
Next, a wafer transfer robot 26 transfers the wafers 16 from the first tank 10a to the second tank 10b. In the second tank 10b, the wafers 16 are immersed in a second ACT solution, which removes residual photoresist from the wafers 16. Finally, the robot 26 transfers the wafers 16 from the second tank 10b to the third tank 10c, where the wafers 16 are rinsed with the acidic NOE solution, which removes additional residual particles from the wafers 16 prior to further processing.
After the wafers 16 are placed in the third tank 10c, the robot 26 typically returns to the load position adjacent to the first tank 10a to receive an additional lot of wafers and place the wafers in the first tank 10a. However, during transit of the robot 26, residual aqueous acid solution 28 which remains on the robot 26 has a tendency to drip from the robot 26 and fall into the ACT solution in the first tank 10a and second tank 10b, through the lid gap 20. Some of the residual aqueous acid solution 28 drips onto the half-lid panels 18 and flows into the tank 10a or 10b through the lid gap 20.
While the NOE solution used to rinse the wafers in the third tank 10c typically contains about 5% water, the ACT organic solvents in the first tank 10a and second tank 10b typically contain monoethanolamine (C2OHNH2), without water. In the event that residual aqueous acid NOE solution 28 falls into the ACT organic solvent, the amino group on the monoethanolamine reacts with the water in the NOE solution to form hydroxide ion, according to the following equation:R−NH2+H2O----->OH−+R−NH3+
The resulting hydroxide ion reacts with and damages aluminum layers and interconnects previously fabricated on the wafers 16. In severe cases, aluminum damage is manifested by peeling of the aluminum layers or interconnects from the wafer 16. Accordingly, a novel interlocking lid for a wet bench is needed to prevent aqueous acid solution from inadvertently dripping from a transfer robot into a basic ACT solution used in the stripping of photoresist from wafers.
Accordingly, an object of the present invention is to provide a novel interlocking lid which is suitable for a wet bench tank.
Another object of the present invention is to provide a novel interlocking lid which substantially prevents a liquid from inadvertently falling into a wet bench tank.
Still another object of the present invention is to provide an interlocking lid which substantially prevents contamination of a liquid in a wet bench tank.
Yet another object of the present invention is to provide a novel interlocking lid which may prevent water-induced damage to metal structures on semiconductor wafers processed in a wet bench tank.
A still further object of the present invention is to provide a novel interlocking lid suitable for a wet bench tank, which interlocking lid may include features that facilitate runoff and prevent or hinder pooling of liquids that fall on the exterior of the lid.
Yet another object of the present invention is to provide a novel interlocking lid which may include a pair of lid panels provided with a clasp for interlocking each other when in a closed position on a wet bench tank.